1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a large cord air cooled turbine rotor blade with cooling flow modulation.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
A gas turbine engine, such as an industrial gas turbine (IGT) engine, includes a turbine with multiple rows or stages or stator vanes that guide a high temperature gas flow through adjacent rotors of rotor blades to produce mechanical power and drive a bypass fan, in the case of an aero engine, or an electric generator, in the case of an IGT. In both cases, the turbine is also used to drive the compressor.
It is well known in the art of gas turbine engine design that the efficiency of the engine can be increased by passing a higher gas flow temperature through the turbine. However, the turbine inlet temperature is limited by the material properties of the turbine, especially for the first stage airfoils since these are exposed to the highest temperature gas flow. As the gas flow passes through the various stages of the turbine, the temperature decreases as the energy is extracted by the rotor blades.
Another method of increases the turbine inlet temperature is to provide more effective cooling of the airfoils. Complex internal and external cooling circuits or designs have been proposed using a combination of internal convection and impingement cooling along with external film cooling to transfer heat away from the metal and form a layer of protective air to limit thermal heat transfer to the metal airfoil surface. However, since the pressurized air used for the airfoil cooling is bled off from the compressor, this bleed off air decreases the efficiency of the engine because the work required to compress the air is not used for power production. It is therefore wasted energy as far as producing useful work in the turbine.
FIG. 1 shows an external heat transfer coefficient (HTC) profile for a first stage turbine rotor blade in an industrial gas turbine engine. As seen in FIG. 1, the airfoil leading edge and trailing edge as well as the forward region of the suction side surface experiences a high hot gas heat transfer coefficient while the mid-chord section of the airfoil is at a lower hot gas HTC than the LE and TE and the forward suction side sections of the airfoil. The suction side TE is represented by the end of the line on the left side of the graph, the low point of the two dips represents the mid-chord sections of the airfoil, the high point on the graph represents the leading edge, and the end of the line of the right side of the graph represents the trailing edge.